How to do vaccuum sealed pack modeling in Blender?
I'm adding another answer because things have changed with Blender 2.82 (which is still in alpha and can be downloaded here). Namely, you can now use pressure inside cloth volumes, including negative pressure.

This makes it much easier to simulate a vacuum sealed pack accurately:


Enable Physics > Collision on your target objects
Model a mesh representing the "relaxed" bag around your objects; give it a good level of subdivision

Select the vertices along the rim, and assign them to a vertex group with a weight of 0.6 - 0.7. 

Another option is to only select one, or three, edges of the rim, to simulate different kinds of bags/vacuum apparatus.

We use this to quickly create a "stiffer" rim. There are however better ways of doing this (like fine-tuning the structural springs parameters instead of the pin groups).
Enable Physics > Cloth on your bag.

Parameters: I've mostly used the defaults, but


the Quality Steps must be higher, around 25
under Shape > Pin group, select the vertex group you created at step 3
under Collision, increase the Quality to around 8, and enable Self collisions
under Field Weights, remove (set as zero) the influence of Gravity

Lastly, select a value around -100 for Cloth > Pressure (in my example I've done it more gradually, going from 0 to -100 over 40 frames, but it turned out to be unnecessary)
Decrease the Cache length to around 40 frames, then Bake


You can now go to the last frame and "Apply" the Cloth Modifier (if you want to get rid of the simulation)